1. Field of the Invention
This invention relates generally to a chemical delivery system that may be used, for example, to deliver a chemical (e.g., sodium hypochlorite, algaecide) to water or effluent within a containment vessel.
2. Description of the Related Art
Chlorinators, which use either solid or liquid disinfectants, are known to the prior art. Illustrative of chlorinators using solid disinfectants are U.S. Pat. No. 6,627,071 issued to Braden on Sep. 30, 2003; U.S. Pat. No. 6,932,912 issued to Chaffin on Aug. 23, 2005; U.S. Pat. No. 6,183,630 issued to Reeves on Feb. 6, 2001; U.S. Pat. No. 4,100,073 issued to Hopcroft on Jul. 11, 1978; U.S. Pat. No. 5,350,512 issued to Tang on Sep. 27, 1994; and U.S. Pat. No. 5,405,540 issued to Tang on Apr. 11, 1995. Illustrative of chlorinators using liquid disinfectants are U.S. Pat. No. 4,333,833 issued to Longley et al. on Jun. 8, 1982; U.S. Pat. No. 4,019,983 issued to Mandt on Apr. 26, 1977; and U.S. Pat. No. 3,996,139 issued to Prince et al. on Dec. 7, 1976.
Disinfection is widely used as part of wastewater treatment systems. In practice, a disinfectant such as chlorine is introduced at a point in the wastewater treatment system after which sufficient time, either by flow into a storage tank or through a region of flow, passes to permit the disinfectant to effectively disinfect the contaminant-bearing wastewater. The amount of disinfectant added to the wastewater is referred to as the “dosage,” and is usually expressed as milligrams per liter (mg/l) or parts per million (ppm). The amount of disinfectant necessary to disinfect a particular volume of wastewater is referred to as the “demand.”
The reaction between the disinfectant and the contaminants is typically not instantaneous but is instead time dependent. In order to obtain adequate disinfection, the mixing of wastewater and disinfectant should be completed in the shortest time possible, ideally a fraction of a second. The amount of disinfectant remaining in the wastewater at the time of measurement is referred to as the “residual.” The residual is therefore determined by the demand subtracted from the dosage.
Prior art chlorinators, whether using a liquid or solid disinfectant, typically mix the disinfectant with the wastewater during the flow of wastewater through the wastewater treatment system. In the case of chlorinators using a solid disinfectant, such as those disclosed in U.S. Pat. No. 6,183,630 issued to Reeves on Feb. 6, 2001; U.S. Pat. No. 4,100,073 issued to Hopcroft on Jul. 11, 1978; U.S. Pat. No. 5,350,512 issued to Tang on Sep. 27, 1994; and U.S. Pat. No. 5,405,540 issued to Tang on Apr. 11, 1995, mixing occurs by wastewater flow about a plurality of disinfectant tablets. In such systems the disinfectant is mixed at a rate that is dependent on the surface area of the tablet in contact with the wastewater, the density of the wastewater and the flow rate of the wastewater, among other variables. In the case of chlorinators using a liquid disinfectant, such as U.S. Pat. No. 4,333,833 issued to Longley et al. on Jun. 8, 1982, mixing occurs at a contactor in the flowline wherein disinfectant fluid is drawn from a reservoir by pressure differential. In such systems the amount of chlorine combined with the wastewater varies with the flow rate of the wastewater and wastewater density.
U.S. Pat. No. 6,627,071 issued to Braden on Sep. 20, 2003 teaches a chlorinator that discharges a uniform volume of disinfectant, but requires a disinfectant tank and a core wall defining a core space and an annular space in the disinfectant tank interior. A check valve limits flow during operation of the pump. After the pump deactivates, the check valve opens to reestablish the quantity of disinfectant fluid within the disinfectant tank.
Many prior-art chlorinators that use liquid disinfectant require an effluent discharge pump to displace fluid through a venturi. That displacement creates a suction that draws a disinfectant into piping where it mixes with the effluent. Such pumps, however, are a significant cost element of such systems, both in terms of the upfront cost of the system and in terms of repairing or replacing the pumps when necessary. Moreover, discharge pumps are not used in all septic systems, meaning that systems such as those described by U.S. Pat. No. 6,627,071 and U.S. Pat. No. 6,932,912 have limited applicability.